T-Mobile has at last merged with Sprint, uniting the nation's third- and fourth-largest carriers and shaking up how some of you may get your wireless service. But this massive shift in the industry brings with it questions for people with T-Mobile and Sprint devices.

With more than 100 million users, the two carriers now have a customer base closer in scale to larger rivals AT&T and Verizon. Having one less wireless player elicited concern from regulators that easing competitive pressure would mean higher prices, but T-Mobile has maintained it would continue to serve as the aggressive "Un-carrier" underdog representing consumers. 

But there will be big changes coming, especially for Sprint customers who all of a sudden have a new provider. From devices and 5G to rate plans and features, here is a breakdown of what you can expect.